The industrial revolution of fossil fuel provided mankind with cheap and accessible energy and fuels. The demands for the fossil based fuels are immerging constantly, owing to the population growth and improvement of life style. But as the petroleum reserves are diminishing constantly, researchers have been readily diverted to utilize renewable biogenic source of energy and fuels. As the innovation in renewable energy; fuel generation form the renewable sources e.g. biodiesel are taking the spotlight of new generation fuel alternative hence the up-gradation of this bio base oil is of tremendous commercial and industrial interest. So, a numbers of effort are made to improve the quality of bio-oil, implies hydrogenation, FCC, isomerization etc.
Bio-oil is basically made up by the component from cellulose, lignin etc. but in order to use as a suitable fuel, it need to be hydrogenated to bust-up the H/C ratio, octane number, calorific value etc. Owing to this, hydrogenation of phenol and phenolic derivatives has paid much attention over a couple of years. As the bio-oil contains high concentration of water so dehydration catalyst should work in both polar as well as nonpolar medium or in biphasic system.
The selective hydrogenation of phenol or phenolic derivatives to its hydrogenate products also have tremendous commercial interest because of the value addition of bio-oil or subsequent synthesis of cyclohexanol and subsequently to produce adipic acid or caprolactum. So the selective hydrogenation of phenol and its derivatives will be the viable process to upgrade the bio-oil and at the same time cyclohexanol and its derivatives can be produced from phenol and its derivatives. The current industrial process for the production of cyclohexanol from cyclohexane produce low yield with vigorous reaction condition. So the hydrogenation of phenol to cyclohexanol can be an alternative process to produce cyclohexanol. There are reports on the production of cyclohexanol or its derivatives by direct hydrogenation of phenol or its derivatives with such a high yield.
Reference can be made to U.S. Pat. No. 4,503,273 by Phillips Petroleum Company, Okla, where they reported the hydrogenation of phenol and phenolic derivatives for the production of useful chemicals. The invention relates to use group VIII metals (namely Ni, Pd, Pt) catalyst with one promoter in organic solvent in presence of a base of about 145-250° C. at 6.8-13.8 MPa H2 pressure. A conversion of 100% of bisphenol was achieved at 200° C. with a selectivity of 75.0-99.9%. But the requirement of high H2 pressure with considerably high temperature make the process costly, other hand the catalyst worked only with organic solvent along with a promoter and base which is also a disadvantage of this process.
Reference can also be made to European patent application EP 1637512 A1, 2006 by Uday Joshi's group to provide a method of hydrogenating phenol, using carbon dioxide and a supported rhodium and/or ruthenium catalyst, to hydrogenate phenol. The drawback of this process is that used 10 Mpa H2 and 10 MPa CO2 pressure. Using such a high pressure required an additional safety arrangement. Moreover, after 2 h reaction 87% cyclohexanol selectivity was obtained at 80° C.
Reference can be made to the article Chem. Commun., 2013, 49, 303-305 in which Duan et al. have shown that Rh—Ni bimetallic catalyst is efficient to convert 54.4% phenol with 71.2 cyclohexanol selectivity. But process is restricted because of the use of cyclohexane as solvent; furthermore the H2 pressure and the reaction time to achieve the conversion and selectivity were also very high.
Reference can also be made to the Chem. Commun., 2004, 930-931, in which Ohde et al. showed the use of palladium and rhodium nanoparticle stabilized in supercritical CO2 for the catalytic hydrogenation of arenes to cyclohexane. They achieved 80-100% arenes conversion with 60-100% product selectivity with the use of different type of plastic supported palladium and rhodium catalyst.
Reference can be made to J. Am. Chem. Soc. 2011, 133, 2362-2365, in which Wang et al. reported the selective hydrogenation of phenolic compound over Pd® carbon nitride in aqueous medium. The disadvantage of the catalyst is the heavy amount of Pd loading; which restrict the catalyst for its industrial use.
Another reference may also be made to Chem. Comm., 2011, 47, 2529-2531 in which hydrogenation of arene was carried out via palladium nanoparticle stabilized by polyvinylpyrrolidone (PVP). A 100% phenol conversion with 99.8% cyclohexanol was achieved at 2 MPa H2 pressure at 60° C. for 2 h. The major drawback of this work is the use of PVP during the reaction; and the separation of PVP from the reaction mixture will be difficult to use this in the industrial level.
Another reference can be made to Chem. Commun., 2008, 999-1001 by Makowski et al. in which they reported the hydrogenation of hydroxy aromatic derivatives over palladium nanoparticle on hydrophilic carbon. They used high amount of Pd (10 wt %) and reaction time was very lengthy (up to 72 h) to get good yield.